1. Field of the Invention
The present invention relates to a lighting system which supplies illuminating light to an end of a light guide for an endoscope.
2. Description of the Related Art
A xenon lamp, which is known as a high-intensity lamp with a low heating value, is widely used as a light source for inputting illuminating light to a light guide of an endoscope. In a state where the xenon lamp is fixed so that the axis thereof extends horizontally, the amount of light emitted from the xenon lamp oscillates in an area above the axial center of the light emitted from the xenon lamp due to the phenomenon of oscillation which occurs at convection or electrical discharge of the xenon gas sealed in the xenon lamp, or due to some other reason.
A small amount of such oscillations present no problem as long as the amount of the light having no fluctuations is relatively greater than that the amount of light having fluctuations when the degree of opening of a diaphragm is great. However, the fluctuations of the light amount show up as flicker in the illuminating light when the degree of opening of the diaphragm becomes small, and such flicker becomes more conspicuous as the degree of opening of the diaphragm decreases. This may obstruct the observing operation of the endoscope.
To prevent such a problem from occurring, there has been proposed a diaphragm device disclosed in Japanese Unexamined Patent Publication No.2001-340293. In this patent publication, as shown in FIG. 4, a pair of right and left diaphragm plates 91 are disposed to be capable of intercepting an optical path A of the illuminating light emitted from a lamp to the incident end of a light guide from the right and left sides of the optical path A, respectively. At least one of the pair of diaphragm plates 91 is provided with a projecting portion 92 which intercepts only an upper portion of the optical path A when the degree of opening of an aperture (i.e., the diaphragm plates 91) of the optical path A is extremely small.
The pair of diaphragm plates 91 are pivoted at a pivot 93 positioned straight above the optical path A. In a state where the degree of opening of an aperture of the optical path A is made extremely small by the pair of diaphragm plates 91, only a light bundle which is passed through a gap between the pair of diaphragm plates 91 which is formed in a vertically-lower half portion of the optical path A is incident on the incident end of a light guide.
In a conventional lighting device for an endoscope such as discussed above, the pair of diaphragm plates 91 must be rotated about the pivot 93 very finely to control the amount of illuminating light incident on the incident end of the light guide when the degree of opening of an aperture of the optical path A is extremely small.
Therefore, when a subject is observed closely through the endoscope, at the time the degree of opening of an aperture of the optical path A is generally made extremely small, even an extremely slight positional error or slight play in a drive system for driving the pair of diaphragm plates 91 tends to cause a substantial error in the amount of illuminating light incident on the incident end of the light guide, which makes the control of that amount of the incident light inaccurate.
Providing the drive system with reduction gearing having a high speed reduction ratio to prevent such a problem increases the number of elements of the drive system, and therefore increases the production cost of the drive system. At the same time, the amount of illuminating light incident on the incident end of the light guide cannot be controlled smoothly due to backlash and play occurring in such reduction gearing. As a result of this, a substantial delay (the extent to which is visually observable) occurs in control of the amount of illuminating light incident on the incident end of the light guide.
The present invention provides a lighting system for an endoscope which does not cause xe2x80x98flickerxe2x80x99 in the illuminating light incident on the incident end of a light guide due to the aforementioned phenomenon of oscillation that occurs at convection or electrical discharge of the xenon gas sealed in the xenon lamp, especially when the degree of opening of a diaphragm of the lighting system is extremely small, and which makes it possible to control the amount of illuminating light incident on the incident end of the light guide smoothly and precisely with a simple structure.
According to an aspect of the present invention, a lighting system for an endoscope is provided, including a lamp for supplying illuminating light, the lamp being positioned so that an optical axis thereof is oriented horizontally; a light guide having an incident end upon which the illuminating light from the lamp is incident; and a diaphragm plate rotated about a pivot so as to advance into and retract from an optical path of the illuminating light, the pivot extending parallel to the optical axis of the lamp and positioned one of above and below the optical path. The diaphragm plate includes a notch which is formed at one end of the diaphragm plate, the notch being positioned along an arc which is centered about the pivot and which intersects a center of the light guide when the diaphragm plate rotates about the pivot. A large number of minute perforations are formed along and below the arc.
It is desirable for the diameters of the large number of minute perforations to vary successively in a predetermined direction.
The large number of minute perforations can be aligned in a plurality of rows along the arc on the diaphragm plate.
The large number of minute perforations can be formed on the diaphragm plate at positions thereon no more than half of a radius of the optical path away from the arc.
It is desirable for the diameters of the large number of minute perforations to decrease in a direction away from the notch.
It is desirable for the diaphragm plate to rotate about the pivot so as to advance into and retract from the optical path in a direction orthogonal to the optical axis of the optical path.
It is desirable for the diaphragm plate to be fixed at one end thereof to a rotating shaft of a drive motor, the notch being formed at the other end of the diaphragm plate.
It is desirable for the pivot to extend parallel to the optical axis of the optical path.
Each perforation of the large number of minute perforations can be circular in shape.
It is desirable for the notch to be formed so as to be substantially symmetrical with respect to the arc, a width of the notch gradually decreasing in a direction along the arc toward an innermost portion of the notch.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2002-27503 (filed on Feb. 5, 2002) which is expressly incorporated herein by reference in its entirety.